The introduction of new services in wireless networks has put a premium on spectral efficiency and coverage in cellular networks. Cellular networks have come a long way since the analog voice telephone systems of the mid 1980s, such as the Advanced Mobile Phone Service (AMPS) or the Nordic Mobile Telephone (NMT) System. The 1990s saw the introduction of second generation (2G) digital cellular technologies such as the Global System for Mobile Communication (GSM) and packet data systems such as the General Packet Radio Service (GPRS) and their evolved third generation versions, Enhanced Data Rates for Global Evolution (EDGE) and Enhanced GPRS (EGPRS) respectively. The need for higher bandwidths and data rates has also led to standardization of the Universal Mobile Telephone Service (UMTS). Third Generation (3G) standardizations of GSM/EDGE and UMTS have been carried out by the 3GPP (Third Generation Partnership Project) whose focus at the time of this invention has been on specifying the High Speed Packet Access (HSPA) service for WCDMA and the OFDM-based evolution of 3G in a standard known as Long Term Evolution (LTE).
Much of the latest work to improve data rates, coverage and capacity has been on the use of multiple antenna technologies such as those illustrated in FIGS. 1A, 1B and 1C. FIG. 1A illustrates multiple antenna elements with physical separation between antenna elements. FIG. 1B illustrates antennas grouped into multiple groups. The physical separation of the antenna elements within a group is less than the separation between the groups. FIG. 1C illustrates a phased array antenna. Space-time Transmit Diversity (STTD), beam-forming and Spatial Multiplexing (SM) or Multiple-Input Multiple Output (MIMO) have been proposed as options in various 3G standard contributions, as well as concepts such as Per-Antenna Rate Control (PARC) or Per-Stream Rate Control and Selective PARC when applied to beam-forming.
Multiple antenna systems work reasonably well in enhancing data rate or coverage and capacity. However, they face some deficiencies in getting the maximum possible gains in performance. First, many multiple antenna technologies rely on the Carrier-to-Interference Ratio (CIR) being sufficiently high in order to realize the performance gains possible. However, mobile terminals that are disadvantaged with respect to the connected base station (e.g., far distance from the base station) may not have such high CIRs.
Second, current state of the art is limited in the ability of these multiple antenna systems to suppress interference levels elsewhere in the cell (or coverage area), while improving desired signal energy towards the terminal that the network is communicating with. This is because simultaneous increase in signal energy in one part of the coverage area while suppressing interference levels in the rest of the coverage area is an ill-formed problem and generally difficult to solve using systematic methods.